1. Field of the Invention
This invention relates to a magnetic bearing type centrifugal blood pump assembly for pumping blood.
2. Prior Art
Several magnetic bearing type pump apparatus for pumping biological fluid such as blood and plasma are known as disclosed in U.S. Pat. No. 5,112,202 and International Publication No. WO 82/3176. These are centrifugal and axial flow turbo pumps of the magnetic bearing type wherein a magnetic member constituting an impeller is position controlled by a magnetic force of an electromagnet so that the impeller may rotate without, contact with any component. These blood pump apparatus have an integral structure that an impeller position control section having an electromagnet and a position sensor (that is, controlled magnetic bearing means) and an impeller rotation torque generating section (that is, uncontrolled magnetic bearing means) are incorporated with a pump housing.
In feeding blood, the most important considerations are to avoid breakage of useful components such as erythrocytes and platelets and to avoid coagulation of blood by reaction with foreign matter. Magnetic bearing type blood pumps having no frictional interface on a surface to come in contact with blood are advantageous in this respect and regarded promising as blood pumps for continuous operation over a long term of the order of months. The magnetic bearing type blood pumps, however, have the problem that the pump is interrupted when a failure occurs in the magnetic bearing means, that is, when the impeller position control section or controlled magnetic bearing means becomes inoperative. Upon such failure, the impeller is magnetically attracted toward the impeller rotation torque generating section or uncontrolled magnetic bearing means, and magnetic attractive forces developed between them prevent the impeller from rotating. Once the pump is interrupted, blood contained therein starts coagulating. It is, therefore, desired to provide the blood pump with a fail-safe mechanism which can maintain rotation of the impeller even when the impeller position control section is inoperative, thereby preventing blood coagulation until the blood pump is replaced by a new one.
It is preferred to minimize thrombus formation within the blood pump during rotation of the impeller enabled by the fail-safe mechanism. In particular, since blood stagnation is likely to occur between the impeller and an inner surface of the pump housing facing the impeller rotation torque generating section, it is necessary to suppress blood stagnation in that area.
Therefore, a first object of the present invention is to provide a centrifugal blood pump assembly which has a fail-safe mechanism allowing the impeller rotation torque generating means or uncontrolled magnetic bearing means to rotate the impeller even when the impeller position control section or controlled magnetic hearing means is inoperative, and minimizes thrombus formation within the blood pump during rotation of the impeller enabled by the fail-safe mechanism.
A second object of the present invention is to provide a centrifugal blood pumps assembly which has a fail-safe mechanism allowing the impeller rotation torque generating means or uncontrolled magnetic hearing means to rotate the impeller even when the impeller position control section or controlled magnetic bearing means is inoperative, and ensures effective rotation of the impeller enabled by the fail-safe mechanism.
As mentioned above, blood transportation requires to avoid damage to useful components such as erythrocytes and platelets and to avoid coagulation of blood by reaction with foreign matter. Magnetic bearing type blood pumps having no frictional interface on a surface to come in contact with blood are advantageous in this respect and regarded promising as blood pumps for continuous operation over a long term of the order of months. However, the conventional blood pump apparatus have an integral structure having electromagnets and sensors combined with the pump body and are thus expensive as disposable blood pumps used in heart surgery completed within several hours or in short term service, for example, of several days. Reuse of such pumps is difficult for the reason of possible infection since the interior comes in contact with blood. The pump apparatus must be discarded in entirety. However, since such used medical instruments are industrial wastes, it is desirable to reduce the amount of used medical instruments discarded when the subsequent disposal is taken into account.
A third object of the present invention is to provide a centrifugal blood pump assembly wherein an impeller rotation torque generating means or uncontrolled magnetic bearing means and an impeller position control section or controlled magnetic bearing means are removably mounted to a blood pump so that only the blood pump which is difficult to reuse may be discarded, and the controlled and uncontrolled magnetic bearing means are reusable. This reduces the amount of used medical instruments discarded as industrial waste.